Systemd, upstart, and System V

SystemdIt is an init software in Linux. It is developed by Lennart Poettering and is open-source under lgpl 2.1 and later versions. Its development goal is to provide a better framework to represent the dependency between system services (English: Service (Systems Architecture) and to achieve parallel startup of services during system initialization, at the same time, it achieves the effect of reducing shell system overhead (English: Computational overhead), and eventually replaces the commonly used System V and BSD-style init.Program. Systemd is the Linux system and service manager compatible with the sysv and LSB initialization scripts. Systemd uses Socket and D-bus to enable the service, provides a daemon-demand startup policy based on the daemon process, retains the process tracking function of Linux cgroups, and supports snapshot and system status recovery, maintains the mount and self-mount points, implements a more refined logical control between services based on the slave relationship, with cutting-edge parallel performance. Systemd can replace sysvinit without any modification. Systemd has been incorporated into many software sources of Linux releases. systora 15 and later versions use systemd as the default INIT program in Linux. (In the feature of Fedora 14, systemd is used as a technical preview. Replace upstart in fedora 15 as the default manager. For more information, see the fedora official documentation and click the link)

SysvinitA daemon (sysvinit package) is a running-level system that uses the running level (single user, multi-user, and more) and links (located in/etc/rc ?. D directory, respectively link to the init script in/etc/init. d) to start and close the system service. The upstart init daemon (upstart package) is an event-based system that uses events to start and close system services.

 

The following are two types of service management commands.

Task	Command	New command
Enable a service automatically	Chkconfig-Level 3 sshd on	Systemctl enable sshd. Service
Disable Automatic startup of a service	Chkconfig-Level 3 sshd off	Systemctl disable sshd. Service
Check service status	Service sshd status	Systemctl status sshd. Service (service details) systemctl is-active sshd. Service (only show whether it is active)
Show all started services	Chkconfig-list	Systemctl list-units-type = Service
Start a service	Service sshd start	Systemctl start sshd. Service
Stop a service	Service sshd stop	Systemctl stop sshd. Service
Restart a service	Service sshd restart	Systemctl Restart sshd. Service

<Table reference self-http://www.talaland.com/systemd-service-configuration/>

Rhel6 uses the newUpstartThe startup service replaces the previous system V init, and upstart is event-driven. Therefore, it only contains the script to be started on demand, which will make the startup process faster. The startup speed of Linux servers that are well-tuned and started using upstart is significantly faster than that of the original system using System V init. RHEL 6 has few changes to the startup process and is compatible with sysv. Therefore, it can still process those changes in the/etc/init directory. D contains services with service scripts. The concept of runlevel also exists in rhel6 <fedora uses systemd, so basically the concept of runlevel does not exist>.

Related Changes in rhel6:

The/etc/inittab is only used to configure the default running level of the system. All entries previously set by the/etc/inittab exist in the/etc/init/directory as a single file.
/Etc/init/RCs. conf sets the initialization of the system by starting most basic services.
/Etc/init/rc. conf
/Etc/init/control-alt-delete.conf defines the system behavior when the user presses the "control-alt-Delete" three keys
/Etc/init/tty. conf and/etc/init/serial. conf define system processing terminal Login
Active_les les in/etc/sysconfig/init determines the creation of the virtual console, whether autoswap automatically detects swap partitions, and the shell used by root in single-user mode. The default value is/sbin/sushell, in addition, the/sbin/sulogin logon prompt is displayed before the single-user mode is enabled.